The present article provides a perspective for computational predictions relating to flow localization under a wide range of deformation rates for a variety of materials characterized by constitutive equations incorporating the strain-rate and temperature sensitivities, and strain-rate-history, temperature-history, and strain-gradient dependences of the flow stress. The regularization schemes to remedy the problems associated with spurious mesh sensitivity and incorrect convergence in finite-element prediction of flow localization behavior are reviewed. Various aspects of flow localization behavior of plane strain blocks with different shapes and sizes under a wide range of tension rate are discussed on the basis of computational simulations.

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Wave propagation through an imperfectly bonded interface between a layer and a half-space of dissimilar elastic solids is considered. Introducing the `jointed' interface as a model of the imperfectly bonded interface, and treating the three cases of incident P, SV and SH-waves impinging on the layer, we have obtained reflection and refraction coefficients of wave energy and have displayed these in graphical forms. A reflected wave of the same mode as the incident wave is the most sensitive to the strength of the interface for almost the entire range of incident angles. Shutting wave energy in the layer is also affected more by the stiffness when wavelength is less than the thickness of the layer.

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In the present paper, the plane problem for three-phase materials formed from three isotropic homogeneous wedges with arbitrary angles is analyzed. In particular, the eigenequation for the three-phase bonded structure analytically derived in the previous paper is used for investigating the effect of the elastic property of the intermediate material on the order of singularity in the stress field near the apex. For the several cases in which wedge angles ψ₁, ψ₂ and ψ₃ are equal and those in which ψ₁+ψ₃ and ψ₂ are constant, the order of singularity in the stress field for different material combinations and that for different wedge angles of regions 1 and 3 are studied in detail.

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Microscopic stress analysis of composite materials is important for evaluating the strength of structures made of composite materials. However, there are many cases in which it is impossible to calculate the stresses of heterogeneous composite materials by means of the finite-element method because of the material's complex geometry. Therefore, heterogeneous composite materials are treated as homogeneous materials. A homogenization method has been proposed to evaluate accurately the microscopic stresses of heterogeneous composite materials. We developed a homogenization analysis system based on a general-purpose finite-element method code. To discuss the efficiency and the accuracy of this system, numerical experiments are conducted. This paper presents a basic study to investigate microscopic stresses of soft composite materials.

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The resin for plastic packaging is experimentally investigated for viscoelastic deformation under various temperature conditions. The elastic constants are represented in terms of temperature conditions. The creep compliance is formulated by a viscoelastic model of four elements. The stress and strain of the resin model during the cooling process are analyzed by the finite-element method with heat transfer analysis. The deformation of a two-layered model of the resin and material in the cooling process is compared with the experimental results. The thermal deformation is predicted well by the analyzed results. The thermal residual stresses of the resin block and the plastic packaging model in the cooling process are also analyzed. The resin block has large thermal internal stress due to the temperature gradient between the outer surface and the central part. The plastic packaging model also contains large thermal stress in the resin as well as at the interfaces among the resin, chip and lead frame.

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An analytical method for the elasto/visco-plastic deformation of axisymmetrical thin shells subjected to thermal loads due to fluid is developed. First, the temperature distribution through the thickness is assumed to be a curve of the second order, and the temperature field in the shell under appropriate initial and boundary conditions is determined using the equations of heat conduction and heat transfer. Secondly, the stresses and deformations are derived from the thermal stress equations. The equations of equilibrium and the relationships between the strains and displacements are derived from the Sanders elastic shell theory. For the constitutive relations, the Perzyna elasto/visco-plastic equations which consider the temperature effect are employed. The fundamental equations derived are numerically solved using the finite difference method. As a numerical example, a simply supported internally pressurized cylindrical shell of aluminum under thermal loading due to fluid is analyzed, and the variations in displacements and internal forces with time are discussed.

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Three-point bending creep behavior of hot-pressed silicon nitride ceramics was investigated at 1170°C. A unique creep constitutive equation consisting of linear and power law terms was proposed, and the numerical calculation programs for determining the parameters included in the constitutive equation and for describing the creep deformation behavior of silicon nitride ceramics at elevated temperatures were developed. The model for interpreting the time-dependent deflection rate and the change in curvature of the beam due to creep under three-point bend loading was also developed, which fitted well the experimental data.

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Anisotropic creep behavior of polycrystalline metals under multiaxial nonproportional repeated loading conditions is modeled from phenomenological points of view. The creep model consists of basic constitutive equations (BCEs) and an auxiliary hardening rule (AUX) to enhance the predictive capability of the BCEs. The BCEs are specified on the basis of a modification of the conventional kinematic hardening model, and they are characterized by a new kinematic hardening variable which is defined as the sum of two component variables ; one represents the back stress in the conventional sense and the other a flow resistance in the opposite direction of the deviatoric stress. The AUX is governed by a memory region in which only the evolution of the back stress takes place. Two different formulations of the AUX are presented. The applicability of the creep model is discussed on the basis of simulations for multiaxial nonproportional repeated creep of type 304 stainless steel at high temperature.

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The basic objective of this study is to establish the material design concepts for the coexistence of good high-temperature mechanical properties and super heat resistance in the systems of ceramic/metal and ceramic/ceramic functionally gradient materials (FGMs). Flexural and fracture toughness tests were conducted on gas-pressure combustion-sintered Cr₃C₂ ceramic and its composites with Ni and TiC (Cr₃C₂/Ni, Cr₃C₂/TiC) in a vacuum environment up to 1200°C using a newly developed materials testing system. Fracture characteristics were investigated on the basis of fracture mechanics and fractography. The toughness of Cr₃C₂ can be improved by the addition of metallic particles. It is found that the principal mechanism of toughness improvement in these composites (ductile-phase reinforced ceramic matrix composites) is attributable to crack-tip plastic blunting by a ductile metallic phase.

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Creep-fatigue tests were conducted with Modified 9Cr-1Mo steel at 600°C in a very high vacuum of 0.1μPa in order to investigate a "pure" creep-fatigue behavior which is free from the environmental effect of the air. On the whole, the time-dependent life reduction occurs when the duration of tension is longer than that of compression. A good correlation was found between the creep-fatigue life and the fracture mode. When the fracture mode is transgranular, no time-dependent life reduction occurs. In contrast, when it is predominantly intergranular, a significant life reduction is observed. The overstress was experimentally analyzed to evaluate the creep-fatigue damage. The relationship between the overstress and the inelastic strain rate can be fitted, being independent of the strain range.

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In relation to the static load rating of silicon nitride bearing balls, the ring crack initiation load P_R of hot isostatically pressed Si₃N₄ balls was investigated experimentally with emphasis on its statistical property. Initiation of a ring crack was detected using acoustic emission (AE) . P_R approximately followed a 2-parameter Weibull distribution with a shape parameter of about 9. An attempt was made to predict the mean and scatter of P_R using bending test data based on the concept of effective area. The predicted values were compared with the experimental results.

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When the ring crack initiation load P_R of ceramic bearing balls is measured at one position per ball, P_R shows considerable scatter as shown in a previous paper. In order to clarify which of the inter-ball variability and the inter-ball variability is responsible for this scatter, a new type of test was carried out in the present study on HIP-Si₃N₄ bearing balls in which P_R was measured at 8 positions per ball. Initiation of a ring crack was detected using acoustic emission (AE). From analysis of variance, it was shown that the scatter of P_R observed when measuring P_R at one position per ball was mainly due to the intra-ball variability or the spatial variation of P_R within one ball.

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The influence of two secondary effects, rotatory inertia and presence of a crack, on the dynamic plastic shear failure of a cantilever with an attached mass block at its tip subjected to impulsive loading is investigated. It is illustrated that the consideration of the rotatory inertia of the cantilever and the presence of a crack at the upper root of the beam both increase the initial kinetic energy of the block required to cause shear failure at the interface between the beam tip and the tip mass, where the initial velocity has discontinuity. Therefore, the influence of these two secondary effects on the dynamic shear failure is not negligible.

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A fracture callus changes in structural characteristics in response to changes in the dynamic loading condition during the fracture healing process. The purpose of this research is to understand the behavior of the intelligent material system during the process. In this paper, the stress wave propagation behavior of the fracture callus is investigated using finite-element analysis to estimate the structural change. It was concluded from the numerical result that the structural changes of the fracture callus relate closely to the differences in mechanical impedances between the constitutive materials in the callus. The result was experimentally verified by means of the fracture model using the femur of a rat.

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In this study, we investigated a noncontact method of measuring plastic strain of metals using laser speckle. This method is based on observation of the change in laser speckle pattern with surface profile change due to plastic deformation. Analysis of the laser speckle pattern is performed on a computer-based image processing system. The relationships between speckle pattern and surface roughness and frequency characteristics of the surface profile were investigated. Surface roughness and surface profile were observed for steel specimens polished with emery paper or plastically deformed. The surface profile diagram was analyzed by means of the fast Fourier transform with a computer and distribution of the spatial frequencies was obtained. The results showed that distribution of light intensity of the speckle is related to frequency distribution of the surface profile, but it is not always related to surface roughness. It was also clarified that the laser speckle pattern is closely related to the magnitude of plastic strain.

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Residual stress was investigated experimentally and analytically in silicon substrates after local thermal oxidation. Shallow trenches about 0.3μm deep were formed before 1000°C oxidation. Residual stress in the substrate after oxidation was measured using microscopic Raman spectroscopy. Tensile stress of about 50MPa initially occurred at the substrate surface. However, the residual stress decreased to zero as the thermal oxide film thickness increased, and then compressive stress increased. The stress development process was analyzed using the finite-element method, and the results showed that three processes were mainly involved : oxidation-induced stress at the curved surface, deflection of the nitride film, which was used as an oxidation protection mask, and constraint of volume expansion of the newly oxidized film. The predicted and measured results were in good agreement for stress changes caused by increasing oxide film thickness.

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A unified constitutive model which can predict cyclic plasticity, uniaxial and biaxial ratchetting, creep, and stress relaxation is required by designers of aeronautic equipment, nuclear reactors and so on. Detailed experimental observation of considering viscoplastic behavior of materials must be carried out to construct a unified constitutive model. In this paper, uniaxial and biaxial ratchetting tests and creep tests were carried out at room temperature and at 550°C using SUS 304 stainless steel. As a result, it is clarified that uniaxial ratchetting behavior is affected by the viscous deformation of the material, and that biaxial ratchetting behavior is affected by both the viscous deformation of the material and the deformation caused by nonproportional loading.

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A method is developed for applying the d-c potential drop technique to simplified nondestructive evaluation of a circumferential 3-D crack on the inner surface of a welded pipe. The pipe is welded circumferentially and the crack exists vertically to the inner surface at the weld. Potential drop is measured on the outer surface of the pipe. The method is based on 2-D theoretical analysis with modification for considering the actual 3-D nature of current flow. In order to determine the shape and size of the crack, measured distribution of the potential drop is compared with the 2-D analysis for a respective segment, which is based on the stream line, in the circumferential direction of the pipe containing an assumed crack. The effect of weld on the potential drop is treated based on the work reported so far. It is shown that the evaluated shape and size coincide well with those of the actual crack.

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In the analysis of sheet metal forming, the constitutive equations are examined with respect to prediction of breakage strains. Breakage initiation is numerically evaluated by the method proposed previously by one of the authors (Gotoh) in which the onset of localized necking is adopted as the breakage condition. Numerical results of limiting strains evaluated by the use of the J 2-Gotoh's corner (J2G) theory and biquadratic anisotropic yield function are in good agreement with experimental results. Next, the commercial FEM code 'JNIKE3D' is improved by introducing them. The evaluation function for breakage is also introduced into the code. A modified radial return method is proposed and adopted as the stress-point integration algorithm for this anisotropic case. As an example, a necking in tensile test is simulated to verify the effectiveness of the improved JNIKE3D.

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The square-cup deep drawing process is numerically simulated by elastic-plastic FEM. J 2-flow theory (J2F), J 2-Goth's corner theory (J2G) and the biquadratic yield function for anisotropy, which were previously proposed by one of the authors, are used as constitutive equations. Friction coefficients on dies are measured using a model test, and the actual pressure distribution on the blank-holder is taken into account in the calculation. Breakage initiation is numerically evaluated by the authors' method, in which the onset of localized necking is adopted as the breakage condition, using the J2G constitutive equation and the biquadratic yield function. Numerical results such as distribution of displacement and strain along the die surface, the punch load, the breakage location, and the punch travel at the onset of breakage are in good agreement with the experimental results.

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